Update

DA sent the prop and their muffler overnight express. Was certainly no need for that but I do appreciate it. Ran about 1/2 gallon through it swapping mufflers and props, see results below.
I am pleased at how this engine has turned into a one flip starter. It runs very well everywhere. The BCM is a bit quieter but the DA sounds more "manly".
Todays results.

Pro-Zinger 22X10
BCM 5900 rpm
DA 6700 rpm

NX 21X10
BCM 6100 rpm
DA 6900 rpm

Mejzlik 22X10
BCM 6300 rpm
DA 7100 rpm

Time to quit playing around with this and mount the engine to the plane. Quite a difference huh? Choose your muffler/prop wisely. This engine will be mounted in a H9 80" cap that should weigh around 15 1/2 lbs.

Dave